Epitaxial growth technique is conventionally used to produce a semiconductor device such as a power device (e.g., IGBT (Insulated Gate Bipolar Transistor)) requiring a relatively thick crystalline film.
In the case of vapor phase epitaxy used in an epitaxial growth technique, a wafer is placed inside a film-forming chamber maintained at an atmospheric pressure or a reduced pressure, and a reaction gas is supplied into the film-forming chamber while the wafer is heated. As a result of this process, a pyrolytic reaction or a hydrogen reduction reaction of the reaction gas occurs on the surface of the wafer so that an epitaxial film is formed on the wafer. The gas generated by the reaction, as well as the gas not used, is exhausted through the outer portion of the chamber. After the epitaxial film is formed on the wafer, the substrate is carried out from the chamber. Another substrate is then placed into the chamber, and then an epitaxial film will be formed on that substrate.
In order to produce a thick epitaxial film in high yield, a fresh reaction gas needs to be continuously brought into contact with the surface of a uniformly heated wafer to increase a film-forming rate. Therefore, in the case of a conventional film-forming apparatus, a film is epitaxially grown on a wafer while the wafer is rotated at a high speed (see, for example, Japanese Patent Application Laid-Open No. 2008-108983).
FIG. 4 is a schematic sectional view showing the structure of a conventional film-forming apparatus using an epitaxial growth technique. It refers to a state in which the substrate is carried out (or placed into) the chamber.
As shown in FIG. 4, a film-forming chamber 201 has a belljar-shaped body 302 arranged on a base plate 301 in the film-forming apparatus 200. A base plate cover 303 is arranged and is detachable from the base plate 301. The base plate cover 303 has a shape and size that can cover the whole of the base plate 301.
The base plate cover 303 may consist of, for example, quartz. The base plate 301 is connected to the belljar-shaped body 302 via a flange 210. The flange 210 is sealed with packing 211. During the vapor-phase growth reaction, the temperature will be very high in the film-forming chamber 201. Therefore, flow channels 203 for circulating cooling water are provided in and around the periphery of the chamber 201 to prevent the thermal deterioration of the flange 210 and pipe 212 (which will be described later).
A supply portion 205 for supplying a reaction gas 204 is positioned in the belljar-shaped body 302. The discharge portion 206 is positioned in the base plate 301. The resulting process gas, after the reaction, and the process gas not used in the reaction are exhausted out of the film-forming chamber 201 through the discharge portion 206.
The discharge portion 206 is connected to a pipe 212 via the flange 210. The flange 210 is sealed with packing 214.
A liner 202 is positioned in the film-forming chamber 201. A rotating shaft 216 and a rotating cylinder 217 positioned on the top of the rotating shaft 216 are arranged in the liner 202. A susceptor 208 is attached to the rotating cylinder 217. The rotating shaft is rotated and as a result the susceptor 208 will rotate via the rotating cylinder 217. During the vapor-phase growth reaction, a substrate 207 is placed on the susceptor 208, and then the substrate 207 will be rotated with the rotation of the susceptor 208.
The liner 202 includes an upper opening into which a shower plate 215 is fitted to act as a gas straightening vane having the function of uniformly supplying the reaction gas 204 onto the surface of the semiconductor substrate 207. The reaction gas 204 flows through the shower plate 215 and flows downward toward the surface of the substrate 207. As a result, a pyrolytic reaction or a hydrogen reduction reaction occurs on the surface of the substrate 207 so that an epitaxial film is formed on the surface of the substrate 207.
The substrate 207 is heated by a heater 209 positioned in the rotating cylinder. The heater 209 is supported by an electrically conductive arm-like busbar 220. The busbar 220 is supported by the heater base 221 positioned at the opposite side of the heater 209, the busbar 220 and a rod electrode 223 are connected by the connecting portion 222. Electricity is conducted from rod electrodes 223 through the busbar 220 to the heater 209. The temperature of the substrate 207 is measured by a radiation thermometer 224a, 224b. 
After the epitaxial film is formed, the process gas in the film-forming chamber 201 is replaced with hydrogen gas or inert gas. The substrate 207 is then carried out the film-forming chamber 201.
The liner 202 has a substrate transfer port 246 and the belljar-shaped body 302 has a substrate transfer port 247. A transfer chamber (not shown) is adjacent to the film-forming chamber 201. When the substrate 207 is carried out the film-forming chamber 201, the substrate 207 is moved upwards by a substrate supporting portion (not shown) in the rotating cylinder 217. A transfer arm 248 of a transfer robot is inserted into the film-forming chamber 201 via the substrate transfer ports 246 and 247. The substrate 207 is then transferred from the substrate supporting portion to the transfer arm 248, and carried out the film-forming chamber 201 through the substrate transfer ports 246 and 247.
When the next substrate 207, on which an epitaxial film would be formed, is carried into the film-forming chamber 201, the transfer arm 248 with the substrate 207 placed upon is inserted into the film-forming chamber 201 through the substrate transfer port 246 and 247. Next, the substrate 207 is transferred from the transfer arm 248 to the substrate supporting portion. The position of the substrate supporting portion is lowered, as a result, the substrate 207 is placed on the susceptor 208.
In a conventional film-forming apparatus 200 the following problems can occur.
The reaction gas 204 passes through the shower plate 215 into the inside of the liner 202 and flows downward toward the surface of the substrate 207. The liner 202 includes the substrate transfer port 246 connected to the substrate transfer port 247. The reaction gas 204 enters into this space formed by the transfer ports 246 and 247 (see FIG. 4) hereinafter referred to as the space C. As a result, it takes a long time for the gas to completely exit after epitaxial film-forming.
It is a possibility to introduce inert gas from the side of the substrate transfer port 247 to prevent the reaction gas 204 remaining in the space C. However, there are concerns that the efficiency of the epitaxial reaction will change as a result of the inert gas.
If the substrate 207 used is large in diameter, accordingly the space C tends to be large. In this situation the amount of reaction gas 204 in the space C increases. Therefore, the above-mentioned problem will become more serious.
The present invention has been made to address these issues. That is, an object of the present invention is to provide a film-forming apparatus and a film-forming method that can reduce the possibility of the reaction gas entering and remaining in the space.
Other challenges and advantages of the present invention are apparent from the following description.